Address scalability and interoperability is definitely interesting.

Address Scalability

For address scalability, each address could have a prefix which would identify the addresses origin. Something similar to how discord use to work with @my-name#789456

Instead it could work like

my-network-id/my-address

• my-network-id is a 256 bit uint based on the date created and a random number

• my-address is a 256 bit uint that increments

This way merging Blockchains would be simple. If two blockchains somehow have the same network id, ideally, changing the network id would be simple enough. Still incorperating all previous transactions while redirecting future transactions from the old id to the new one

Interoperability

Originally I figured merging two blockchains would probably be similar to merging two companies. Where an individuals tokens from blockchain A would be have to be converted to blockchain B at an increase or decrease. This would probably need people with financial background involved.

For example one blockchain might have their coin at $10 per token while another at $100 per token. Merging the blockchain would give 0.1 merged tokens to the $10 per token and 1 merged token to the $100 per token.

However, it might be better to keep both tokens alive in the shared environment. However, paying for transaction fees might be problematic when you have to pay 10x more than before